Drilling mud



Patented Sept. 5, i944 UNITED s'r nnnme Mun Donald 0. Bond, Northbrook, lll., assignor to The Pure Oil tion of Ohio B D ago, 111., a corpora:

No Drawing. Application June 4, 194a,

Serial No. 489,701

14 Claims. (Cl. 252-85) -This invention relates to drilling wells and is primarily concerned with the production of an improved drilling mud and composition for preparation thereof for use in .the drilling of wells, especially oil and gas wells, and with the method of drilling wells wherein such muds are used. This application is a continuation-in-part of my co-pending application. Serial No. 303,024,

filed November 6, 1939, entitled Improved drilling mud.

Drilling operations are usually conducted in the presence of a circulation of mud. that is.

water containing mineral matter such as clay in a finely divided ol' 'deflocculated state. Such of the drill hole to prevent either flow of water or gas from the subsurface formation into the drill hole or to prevent loss of drilling fluid from the hole into the formations through which the hole is drilled. These muds are frequently made from material native to the formation in which the well .is drilled, although it is often necessary to add additional material to the mud which will increase the specific gravity in order to increase the weight of the column of mud in the welland thereby offset the effect of high gas pressure. For this purpose weighting materials such as iron oxide and barytes are commonly used. Every natural clay contains particles of many orders of magnitude, some being coarse enough to settle out of a water suspension quickly and others being fine enough to stay suspended for indefinite periods. In a clay that is considered good for drillingepurposes the fine material is predominant and is in an indefinitely which it is dispersed. which in the case of muds, is generally water. The sta- 'bility of colloidal dispersions is also directly related to the charges on the dispersed particles. In general it may be said that strongly charged negative or positive particles form stable dispersions, whereas weakly charged or neutral particles tend to 'flocculate and settle out of the disperse medium.

when drilling in some formations such as, for

example, certain shale formations, considerable difliculty has been experienced due to the property of these shale formations of swelling and sloughing when contacted with water or ordinary drilling mud. This property of some formations to hydrate or absorb water and swell sometimes occurs to such an extent that the holes cave and fill to such a degree that in the end the drilling has to be abandoned. Formations which have this property of absorbing water and swelling are, in the well drilling art, generally termed heaving-shale" formations and it is with these types of formations that this invention is particularly concerned.

It is an object of-this invention to provide an improved composition useful in the preparation of drilling mud.

It is another object of this invention to provide an improved drilling mud which will prevent fine. state of subdivision, the finest being so small of dispersion is termed "deflocculation and a I decrease in the state of dispersion is termed "flocculation." Flocculated clay may be in an equally finely divided state to that of deflocculated clay but the flocculated material will come together in floccuient, loose clumps or aggrethe heaving of heaving-shale formations.

It is a still further object of this invention to provide a drilling mud in which the colloidal mineral content is dispersed as positively charged particles. A further object of this invention is to provide an improved method for drilling in heavingshale formations. I I

Various other objects and advantages will appear as the description of the invention proceeds.

Colloidally dispersed clay, obeying the general rules of colloidal dispersions, carries an electrical charge. Practically all naturally occurring finely divided clays such as kaolin and bentonite carry charge.

negative charges on the dispersed particles when dispersed in an aqueous medium. It is known that the shale in heaving-shale formation is generally betonitic in character and that upon being dispersed in water carries a negative It has now been found that if the colloidally dispersed-particles, generally clay. in

. drilling muds are positively instead of negatively charged. the swelling of heaving-shale can be prevented or lessened too. great extent. ,In the preparation of drilling mud itis gengates which settle readily from in erally desirable to usea iinely divided solid which will have a high colloidal dispersion inwater so 'as to produce a viscous, relatively stable mud with a minimum amount of solids. Bentonite has the aforesaid property and has been found to be a particularly satisfactory clay for use in drilling mud. Like other similar clays, bentonite carries a negative electrical charge when colloidally dispersed in an aqueous medium.

It has been found that such negatively charged colloids may be changed to positive colloids by the in vention may contain weighting materials such as addition of one or more suitable water soluble barytes and antifoaming agents such as diglycol chemical compounds from the group: 'salts of laurate, and also materials which improved stametals wherein the positive valence is three or bility, gel strength and filtration characteristics more, such as thorium, aluminum, cerium and of the mud such as wheat flour and starch. lanthanum salts; acid proteins such as acid gela- It is preferred to use water soluble acid gelatin tin or casein; basic dyes such as methylene blue, and/or acid casein in quantities somewhat in exmethylene green, methylene grey, methyl violet, cess of the quantity requ t impart a positive Bismarck Brown R, Rhodamine B, acrifiavine, charge to the colloidally dispersed solid particles chrysoidin Y and chrysoidin R. By the addition in the drilling mud. The amount of acid protein of one or more of th foregoing matrials, the negrequired to produce positive charged particles atively charged colloidal clay or bentonite may be may be readily determined by the Burton appara- T'irst neutralized and flocculated and upon a furtus or other similar testing devices. ther addition, the neutralized clay may be defloc- When two materials of opposite electrical culated and remainin a stable dispersed state as charge react, the amount of each which is afpositively charged particles. It is not desirable to footed is inversely proportional to the proportions use the flocculated, neutralized particles in drill- 'of replaceable base which is present in a given ing mud since these particles are not stably disweight of each material. In View of the variapersed, the particles readily settling from an tions in the amount of replaceable base in the aqueous dispersion medium. -When such a posivarious dispersed particles, such as bentonitictlvely charged clay as, for example, bentonite, is clays, and in view of the varying degree of ether:- dispersed in water and used'as drilling mud, the tiveness with which acid gelatin and acid casein shale in heaving-shale formationsfdoes not swell impart positive charges to colloidally dispersed or slough off into the hole and the bentonite parparticles, it is apparent that the relative quantity ticles remain stably dispersed. The ability of the used may vary over a rather wide range. The positively charged bentonite to prevent swelling amount of acid casein or acid protein required in of the shale is believed to be due to neutraliza each case may be readily determined by a catation of thenegative charges on the shale particles phoresis test which should be somewhat in excess in the subsurface formation by the positive of that amount required to impart a positive charges on the bentonite in the drilling mud with charge to the dispersed particles. In general the resultant formation of a flocculated film of shale amount of acid casein or acid protein used will and bentonite on the exposed surface of the shale fall between the ranges of 1 part of casein or proformation in the bore hole. The flocculated matein-{o 10 parts of dry bentonite, to 3 parts of terial forms an extremely coherent layer and adcasein or gelatin to 1 part of dry bentonite. The heres tightly to the surface of the formation, thus casein or gelatin may be mixed with the bentonite substantially preventing further neutralization of 4A in the dry state and the mixture subsequently discharges between the clay ofthe shale formation persed in water as required, or they may added and the bentonite in the drilling mud and at the dry or in the dissolved state to mud in WhlCh the same time substantially preventing the ingress of bentonite is already dispersed. further water to the formation, thereby prevent- The term "bentonite as used herein is used ing hydration and swelling of the heaving shale. in a generic sense as including all clays having number of bentonite S p s were made highly colloidal characteristics whether they are incorporating acid protein in order to determine true bentonite or not. Acid gelatin and acid proe Stab ty of such suspensions. The data obtein may be used in the invention, whether or not tained on the suspension is given in the followcompletely soluble in water so long as they are ing table: 5: sufliciently soluble or dispersable in water to pro- Table Ssa'tr;

I I1 g? gg Protein p r te ii Amount of H10 Stability Charge beeitonite solution I suspension 1 5% acid gelatin solution (pH-3.3).... Positive None.

3 Positive.

.8 None.

The protein in each case was made acid by addition of hydrochloric acid. It will be understood, however, that any acid-may be used for imparting an acid conditioirto the protein.

duce deflocculated bentonitic mud which is positively charged.

While an effort has beeinmade to explain the theory by which the positively chiarged colloidal ticles.

particles in drilling mud provide drilling mud which prevents the heaving of heaving-shale formations, it will be understood that the invention theory of tin and acid casein to impart to the bentonite a operation an aqueous mud containing positively charged suspended mineral particles to which the positive charge has been imparted by an acid protein selected from the group consisting of acid gelatin and acid casein. I

, 2. In the drilling of earth bores, the step of circulating through the bore during the drilling operation, aqueous 'mud containing normally negatively charged colloidally dispersed particles and suflicient acid protein selected from the group consisting-of acid gelatin and acid casein to impart a positive charge to said; particles.

3. In the drilling of earth bores, the step of circulating through the bore during the drilling operation an aqueous mud containing suspended bentonite and weighting material and suillcient acid protein selected from the group consisting of acid gelatin and acid casein to impart a positive charge to the bentonite.

4. A composition for use in well drilling mud comprising comminuted bentonite and an acid protein selected from'the group consisting of acid gelatin and acid casein in sufficient quantity to impart a positive charge to the bentonite when suspended in an aqueous medium.

5. A drilling mud comprising an aqueous suspension of normally negatively charged solid particles and suilicient acid protein selected from the group consisting of acid gelatin and acid casein to impart a positive charge to said par- 6. A drilling mud comprising an aqueous suspension of bentonite and suflicient acid protein Selected from the group consisting of acid gelapositive charge.

7. A drilling mud in accordance containing barite.

8. A drilling mud comprising an aqueous suspension of positively charged solid mineral particles of colloidal size to which the positive charge has been imparted by an acid protein selected from the group consisting of acid gelatin and acid with claim 6 casein.

9. A composition useful in the preparation of drilling muds comprising a mixture of bentonite and acid protein selected from the group consisting of acid gelatin and acid casein, the acid protein being present in amount sufllcient to impart to the bentonite particles a positive charge when suspended in water.

10. A composition useful in the preparation of drilling mud comprising comminuted solid particles having a negative charge when suspended in water and sufficient acid protein selected from the group consisting of acid. gelatin and acid casein to impart a positive charge to said particles when suspended in water.

11. A drilling mud in accordance with claim 6 contains from 1 part of acid protein to 10 parts of dry bentonite to 3 parts of acid protein to 1 part of dry bentonite.

12. A composition in accordance with claim 9 which contains from 1 part of acid protein to 10 parts of dry bentonite to 3 parts of acid protein to 1 part of dry bentonite.

13. The steps in accordance with claim 3 in which the mud contains an anti-foaming agent and a material which improves the stability, gel strengthand filtration characteristics of the mud.

14. A composition in accordance with claim 10 including a weighting material, an anti-foaming agentand a material which improves the stability, gel strength and filtration characteristics of the mud.-

c. BOND. 

